1. Field of the Invention
The present invention relates to semiconductor laser apparatuses comprising laser devices.
2. Description of the Background Art
With recent improvements in the performance of personal computers and multimedia equipment, the amount of information to be processed has significantly increased. The increase in the amount of information has led to the development of optical recording media and drives thereof that can handle increased speed and capacity of information processing.
Specific examples of such optical recording media include compact disks (hereinafter referred to as CDs) and digital versatile disks (hereinafter referred to as DVDs). Specific examples of drives for playing back and recording such optical recording media include semiconductor laser apparatuses for the CD and semiconductor laser apparatuses for the DVD. A semiconductor laser apparatus for the CD is capable of emitting an infrared laser beam (wavelength: around 790 nm) for use in playing back or recording the CD. A semiconductor laser apparatus for the DVD is capable of emitting a red laser beam (wavelength: around 658 nm) for use in playing back or recording the DVD.
In the specification, the semiconductor laser device that emits an infrared laser beam (wavelength: around 790 nm) is referred to as an infrared semiconductor laser device, and the semiconductor laser device that emits a red laser beam (wavelength: around 658 nm) is referred to as a red semiconductor laser device.
Among the drives of the optical recording media is a semiconductor laser apparatus capable of playing back or recording the CD and DVD. This semiconductor laser apparatus that comprises an infrared semiconductor laser device and a red semiconductor laser device is capable of emitting an infrared laser beam for the CD and a red laser beam for the DVD.
Using such a semiconductor laser apparatus enables a smaller parts count than using both a semiconductor laser apparatus for the CD and a semiconductor laser apparatus for the DVD, thus resulting in a simpler optical recording medium drive.
Both of an infrared semiconductor laser device and a red semiconductor laser device can be formed on a GaAs substrate. Accordingly, a monolithic red/infrared semiconductor laser device is fabricated by forming both the infrared semiconductor laser device and the red semiconductor laser device on a GaAs substrate as a single chip. Providing the monolithic red/infrared semiconductor laser device in the aforementioned semiconductor laser apparatus enables an interval between the emission points of an infrared laser beam and a red laser beam to be accurately controlled.
Meanwhile, in order to improve the recording density of optical disk systems, semiconductor laser devices that emit a blue-violet laser beam with a short lasing wavelength (wavelength: around 400 nm) have been developed for the next-generation DVD. Semiconductor laser apparatuses that incorporate such semiconductor laser devices emitting blue-violet laser beams have also been developed.
In the specification, a semiconductor laser device that emits a blue-violet laser beam (wavelength: around 400 nm) is referred to as a blue-violet semiconductor laser device.
Unlike the infrared semiconductor laser device and the red semiconductor laser device, the blue-violet semiconductor laser device is not formed on a GaAs substrate. It is thus very difficult to integrate the blue-violet semiconductor laser device with the infrared semiconductor laser device and the red semiconductor laser device into a single chip.
For this reason, JP 2001-230502 A, for example, suggests a semiconductor laser apparatus which is fabricated as follows. Infrared and red semiconductor laser devices are formed on the same chip to fabricate a monolithic red/infrared semiconductor laser device, while a blue-violet semiconductor laser device is formed on a separate chip. Then, the blue-violet semiconductor laser device chip and the monolithic red/infrared semiconductor laser device chip are stacked on each other.
The semiconductor laser apparatus disclosed in JP 2001-230502 A is described. FIG. 50 is a schematic diagram showing the semiconductor laser apparatus 900 according to JP 2001-230502 A.
As shown in FIG. 50, a blue-violet semiconductor laser device 901 is bonded on a support member 903a integral with a package body 903 through a fusion layer 905. The blue-violet semiconductor laser device 901 is connected with the support member 903a mechanically and electrically.
An electrode 901a and an insulating layer 904 are formed on a portion of the blue-violet semiconductor laser device 901. The electrode 901a is formed on the insulating layer 904. An infrared semiconductor laser device 902a is bonded on the electrode 901 through a fusion layer 906, and a red semiconductor laser device 902b is bonded on the electrode 901b through a fusion layer 907.
The infrared semiconductor laser device 902a and the red semiconductor laser device 902b constitute an integrated semiconductor laser device 902 that is monolithically integrated on the same substrate. An electrode 902c is formed on the integrated semiconductor laser device 902.
The electrode 901a, which is connected with the infrared semiconductor laser device 902a, is formed on the blue-violet semiconductor laser device 901 with the insulating layer 904 interposed therebetween. This allows either of the infrared semiconductor laser device 902a and the red semiconductor laser device 902b to be driven independently.
Power supply pins 909a, 909b, 909c are formed so that they are isolated from the package body 903 through respective insulating rings 908a, 908b, 908c. 
Note that the electrode 901a is used as a p-electrode for the infrared semiconductor laser device 902a, the electrode 901b is used as an n-electrode for the blue-violet semiconductor laser device 901 and a p-electrode for the red semiconductor laser device 902b, and the electrode 902c is used as an n-electrode for the infrared semiconductor laser device 902a and the red semiconductor laser device 902b. 
The electrodes 901a, 901b, 901c, respectively, are connected to wires JWa, JWb, JWc through the power supply pins 909a, 909b, 909c. The support member 903a receives power from the power supply pin 903b connected to the package body 903.
The semiconductor laser apparatus 900 in FIG. 50 is thus capable of selecting any of the infrared, red, and blue-violet laser beams, and emitting the selected laser beam.
FIG. 51 is a circuit diagram showing electrical wiring of the semiconductor laser apparatus 900 in FIG. 50.
As shown in FIG. 51, in order to drive the blue-violet semiconductor laser device 901, a negative voltage must be applied to the power supply pin 909b with respect to the package body 903 which is generally grounded when used. In order to drive the red semiconductor laser device 902b, a voltage that is higher than the voltage at the supply pin 909c must be applied to the power supply pin 909b. Further, in order to drive the infrared semiconductor laser device 902a, a voltage that is higher than the voltage at the power supply pin 909c must be applied to the power supply pin 909a. 
Therefore, when driving each of the semiconductor laser devices in the semiconductor laser apparatus 900 in FIG. 50, control of the drive voltage thereof is complicated.
Moreover, when driving the infrared semiconductor laser device 902a by alternating voltage, the insulating layer 904 in contact with the electrode 901a in FIG. 50 functions as a dielectric as indicated by the broken line in FIG. 51. This may cause a current to flow in the red semiconductor laser device 902b through the insulating layer 904 to degrade the high frequency characteristics of the infrared semiconductor laser device 902a. 